1. Field of the Invention
The present invention relates to a temperature compensating method of laser power in an optical disk storage apparatus. More particularly, the present invention relates to a temperature compensating method of laser power in an optical disk storage apparatus whereby input current supplied to a diode can be compensated in response to temperature changes to thereby enable to output a constant laser power in an optical disk such as a compact disk (CD) or a digital versatile disk (DVD) for recording and reproducing a predetermined information by laser.
2. Description of the Related Art
An optical disk storage apparatus for driving a laser diode provided at optical pickup outputs a laser. The laser outputted by the laser diode is irradiated on a surface of the optical disk such as a CD or a DVD serves to record or reproduce a predetermined data.
In the case that data is recorded on the optical disk by the optical disk storage apparatus, the laser diode is driven to irradiate a very high powered laser on the optical disk. In other words, the optical disk is disposed with a recording layer for storing a predetermined data. The storage of data is made possible by change of physical properties of the recording layer, for the physical properties of the recording layer can be changed by high laser power.
In the case that the data recorded on the optical disk is to be reproduced, data pattern formed in the course of recording the data on the optical disk should not be damaged such that the laser diode is so driven as to output a lower laser power than that of recording the data.
If the laser power is changed in the course of recording the predetermined data on the optical disk, the laser pattern recorded on the optical disk is not constant, such that a decreased recording quality containing lots of errors occurs. The decreased recording quality in turn generates degradation of reproduction performance where stored data is not accurately reproduced.
Another disadvantage is that if the laser power is not constantly maintained even during the predetermined data stored in the optical disk being reproduced, a reproduction signal level of the data is changed to disable the optical disk from reproducing a stable data.
Accordingly, the optical disk storage apparatus is typically disposed therein with an automatic power control (APC) to enable to constantly maintain a laser power outputted from the laser diode.
The APC is generally referred to a technique for controlling an accurate output of laser power desired by a laser diode. The APC can now maintain an accurate and exact laser power by adopting a digital control method from an analogue control method.
In general, the performance of a laser diode may generally be inversely related to the ambient temperature. In other words, the laser power outputted from the laser diode is decreased if the ambient temperature is high while the laser power from the laser diode is increased if the ambient temperature is low.
Consequently, the input current supplied to the laser diode is increased if the ambient temperature is high, and if the ambient temperature is low, the input current supplied to the laser diode is decreased so that laser power outputted from the laser diode should be constantly maintained.
In order to output a laser power desired by a laser diode, the APC should provide an Equation of an input current under a particular temperature, i.e., a normal temperature against a voltage of laser power outputted by the laser diode, and it should be beforehand stored in an optical storage apparatus.
Furthermore, if the laser diode is to be driven, the pre-stored Equation is used to calculate an input current for outputting a voltage of the laser power desired by the laser diode. The calculated input current is then supplied to the laser diode to allow the laser power wanted by the laser diode to be outputted.
As mentioned above, the laser diode is such that the laser power is variable in response to changes of the ambient temperature. However, the APC is pre-stored with an Equation relative to an arbitrary temperature, and calculates an input current of the laser diode for outputting the desired laser power by way of the stored Equation. In other words, no consideration is given to the laser power outputted from the laser diode in response to the changing ambient temperature.
As a result, an input current capable of outputting a laser power wanted by a laser diode relative to a particular temperature corresponding to the Equation can be accurately calculated and can be supplied to the laser diode. However, there is a problem in that, if the ambient temperature of the laser diode changes, it cannot be coped with, and, as a result, an input current capable of outputting a laser power desired by the laser diode cannot be accurately set up in response to the changed ambient temperature.